In the 'the back rooms story', since it's more about the experience of being in the strange back rooms space, the main 'characters' could be considered anyone who 'no - clips' into it. They are usually unnamed victims or explorers. They don't have a lot of backstory in the traditional sense. Their main characteristic is that they are in this nightmarish place and are trying to either escape or figure out what is going on. So it's not like a story with a hero with a detailed backstory or a specific goal other than survival and getting out of the back rooms.
Well, the 'the back rooms story' doesn't really have the typical kind of main characters you'd find in a regular story. Instead, it focuses on the people who find themselves trapped in the back rooms. These could be anyone from a random office worker who was in the wrong place at the wrong time and slipped through a reality glitch, to an adventurous soul who was exploring an abandoned building and ended up in this strange dimension. Their common trait is that they are now in this liminal, yellow - roomed, and often dangerous space, and they are all facing the same challenges of survival and finding a way out.
There isn't really a set list of traditional main characters in the 'the back rooms story'. It's more about the people who end up in the back rooms, who are often ordinary individuals thrust into this strange and terrifying situation.